Though the peacekeeping forces travel in armored vehicles, the guerrilla fighters can inflict casualties. The psychological trauma of knowing an ambush can happen at any time makes life tough for the AU soldiers from several countries who battle the al-Shabab rebels allied to al-Qaida.

“They try to ambush us in such places. It’s not easy. We must pass here with vigilance,” an AU soldier groaned as he peered through the bulletproof glass of an armored personnel carrier.

AU troops in August forced al-Shabab out of the capital, Mogadishu. Earlier this year Ugandan and Burundian troops began taking control of suburbs of the capital. Now they are moving far to the northwest in an attempt to secure a supply line from Mogadishu to the former al-Shabab stronghold of Baidoa. Many of al-Shabab’s top foreign fighters are said to have fled to Yemen already.

But the rebels remaining continue their attacks. A week ago al-Shabab fighters ambushed a convoy, wounding one soldier. As the AU area of control widens, the challenges of holding the new territory increase.

There are about 17,000 troops in the AU force, including soldiers from Kenya in the south of the country. With so few troops to control such a wide area, they are relying on public support to keep roads safe from roadside bombs.

“A friendly population is better than tanks,” said Capt. Henry Obbo. “They are driving a dying horse. Public support is with us now.”

Yet in rural villages, residents silently stare at troops. A soldier’s wave typically gets no reaction, except from children. Insurgents often kill suspected supporters of the Somali government, so even waving can invite trouble. But executions, floggings and strict social rules cut down the militants’ public support.

“Al-Shabab was in no way good for us. They conscripted our children and forcibly extorted our farms. They made life hell for us,” said Abdullahi Yassin, an elder in the town of Walaweyn. He said his area has neither the security nor the aid it hoped to see from Mogadishu’s weak government.

“No difference yet, except a little freedom,” he said of al-Shabab’s ouster.

Late last week, African Union forces and Somali troops captured the Blidogle airport, about 100 kilometers (60 miles) northwest of Mogadishu. The troops intend to open the road all the way to Baidoa, about 250 kilometers (155 miles) northwest of Mogadishu, said Hussein Arab Isse, Somalia’s defense minister, speaking at the airport.